The invention relates to the waste treatment of metal containing solutions and, more particularly, to reducing the amount of metal in a spent electroless metal plating solution to allow discharging the solution into a waste system.
The waste treatment of contaminant effluent solutions is a well-known environmental and economic problem which government is attempting to control by setting vigorous standards for their discharge into waste systems such as sewage plants and waterways.
Metal containing solutions represent a large part of the effluents requiring waste treatment with a major source being electrolytic and electroless metal plating processes. Existing waste treatment processes include precipitation, evaporation, ion exchange and electrolysis and a number of patents have been granted relating to these methods.
U.S. Pat. No. 4,420,401 relates to the waste treatment of electroless nickel and copper solutions and a number of representative plating solutions are noted therein, the contents of this patent and the patents shown on lines 65 and 66 of column 1 being hereby incorporated by reference. The disclosed process treats waste spent electroless solutions, which contain metal ions, complexing agents, reducing agents, pH adjusters and other conventional additives such as stabilizers, brighteners, etc. The first step is to ensure that the solutions are capable of electrolessly plating by adjusting the pH and/or adding sufficient reducing agents to enable plate-out of the metal ions. A seeder comprising a particulate material of large surface area having a catalytic noble metal absorbed on its surface is contacted with the solution and the metal ions decompose and plate out on the seeder which is then removed from the solution. The prior art method disclosed in the patent was to load the solution with a material catalytic to the plating reaction causing the solution to undergo spontaneous decomposition and precipitation of the metal.
U.S. Pat. No. 4,425,205 describes a regeneration process wherein a part of the electroless plating bath is treated with a palladium catalyst to precipitate and remove copper. The solution is then treated with acid to precipitate the chelating agent, with the precipitated chelating agent slurry electrolyzed and recycled to the electroless plating bath as a copper complex compound.
A chemical method for precipitating copper, nickel and cobalt from spent electroless plating solutions using sodium hydrosulfite is shown in U.S. Pat. No. 3,770,630.
Using a somewhat novel technique to remove metals from solutions, U.S. Pat. No. 3,755,530 injects droplets of the spent electroless plating solution into a refrigerant to quick-freeze them, followed by removal of ice (water) by sublimation in a controlled vacuum. U.S. Pat. No. 4,144,149 eliminates the metal solubilizing complexing ability of the chelating agent by electrolysis and precipitating metallic copper from the solution. U.S. Pat. No. 4,428,773 removes copper from electroless solutions by heating the solution in a titanium vessel with stirring and the bubbling of air until copper and copper oxide precipitates are formed. The use of ion exchange resins to remove copper from electroless solutions is shown in U.S. Pat. No. 4,666,683.
While the prior art processes reduce the metal content of the plating solutions, the need still exists for efficient and economical methods for waste treating the solutions.